Difference between revisions of "Terminology/it"

Revision as of 15:41, 4 November 2013

In KSP, ci sono molti termini relative alla fisica e a come orbitae, che spesso possono essere fonte di confusione per i non tecnici. Inoltre, vari altri termini e abbreviazioni scientifiche sono utilizzati per descrivere termini comuni. Questa scheda è progettata come una tabella di ricerca concisa di termini necessari per aiutarvi a iniziare la strada per essere un astronauta a pieno titolo!

Matematici

Sistema di coordinate Cartesiane - Uso delle coordinate rettangolari

Sistema di coordinate polari - Uso degli angoli

Ellisse

Di forma ovale, spesso in riferimento alla tua orbita.

Vettore normale

Un vettore perpendicolare al piano.

Scalare

Un singolo valore senza direzione. Gli scalari sono seguiti dall'unità di misura che dice quello che la dimensione scalare riferisce. eg 3m/s, 3 e 3 sono scalari: sono le unità che denotano velocità, cioè lunghezza/distanza, e tempo rispettivamente.

Vettori

Un'insieme di direzione e valore. Come un vettore viene espresso dipende da quale sistema di coordinate si usa e quante dimensioni sono prese in considerazione. <35°, 12> è un vettore polare a due dimensioni, dove <14, 9, -20> è un vettore Cartesiano a tre dimensioni. Ci sono altri sistemi di coordinate ma questi sono i più utilizzati.

<35°, 12> rappresenta una freccia lunga 12 unità, partendo dall'origine (zero, l'angolo non importa perchè un punto non ha dimensioni) e una fine nel punto a 35° dal asse base (tipicamente l'asse x, gli angoli sono positivi in senso antiorario)

<14, 9, -20> rappresenta una freccia partendo dall'origine (<0,0,0>) e una fine nel punto dove la coordinata x è 14, la coordinata y è 9 la coordinata z è -20.

Il vantaggio di utilizzare le coordinate Cartesiane è che si sa esattamente dov'è la posizione finale, ma è più difficile da capire la traiettoria, in coordinate polari invece è facile per trovare la traiettoria, il lato negativo è che si conosce più difficilmente la posizione finale.

Le seguenti qualità fisiche sono tutti i vettori: velocità, accelerazione, forza

A sistemi di coordinate 3D ha bisogno

• Un punto di riferimento. Questa è l'origine.
• 3 vettori-base. Questi definiscono l'unità base di misura rispetto all'origine, sono gli assi x,y e z.

Termini per Orbitare

Visualization of the most common orbital parameters

Apoapsis

In an elliptical orbit, the point of the orbit farthest from the body being orbited.

Periapsis

In an elliptical orbit, the point of the orbit closest to the body being orbited.

Peri-* and Apo-*

When speaking of orbits, oftentimes the words "periapsis" and "apoapsis" will be modified to specify which planet or moon the orbit is around. For example, -kee and -kerb are both commonly used to describe orbits around Kerbin, resulting Perikee/Perikerb and Apokee/Apokerb.

Ascending node

The point at which the orbit crosses the reference plane moving north. Here, "north" means the direction of the orbit normal of the reference plane.

Descending node

The point at which the orbit crosses the reference plane moving south.

Eccentricity

${\displaystyle {\text{ecc}}=1-{\frac {2}{{\frac {Ap}{Pe}}+1}}}$

A scalar describing how non-circular an orbit is.

• ecc = 0 → circular orbit.
• 0 < ecc < 1 → elliptical orbit.
• ecc = 1 → parabolic orbit - this is an escape orbit.
• ecc > 1 → hyperbolic orbit - this is an escape orbit.

Inclination

The angle between an orbital plane relative to a reference plane (e.g. an orbit with 90° inclination to an equatorial reference plane would be called polar).

Low orbit

An orbit that is only just high enough to indefinitely avoid succumbing to hazards of the body being orbited, such as atmospheric drag. Low orbits are used as stepstones, after ascent and before burning to another rendezvous object (planet or vessel), as it allows the exit burn to be performed in any direction and requires the least amount of fuel to reach from the body's surface. A low orbit for Kerbin is typically between 80km and 100km. Bodies with no atmosphere can theoretically allow an orbit at any height above the ground, but below 10km the risk of crashing into mountains or other elevated terrain becomes very high. The time warp is restricted to lower values while in low orbits.

Orbital nodes

Specific points of reference in any orbit such as Apoapsis, Periapsis, intersect points with other orbits etc.

Orbit normal

A normal vector of the Orbital Plane. Produced by cross multiplying the ship's velocity and gravity. Since this follows the right hand rule, from a perspective where the ship is orbiting counter-clockwise it will point "up", while for a ship orbiting "clockwise" it will point down. "Up" is also often labeled as "North" or "N+", and in tandem with that "Down" is labeled "Anti-Normal", "South" or "N-".

Orbital plane

The imaginary disk described by the path of an orbit around a body (commonly used when describing inclinations).

Prograde

The direction in which a ship is traveling along its orbital path. Since orbits are elliptical, it is always tangent to the orbit at the point where the ship is.

Retrograde

The reverse of Prograde, backwards along the orbital path.

Reference plane

Any plane used as a reference for describing your current orbit. For local orbits around a planet, this is often the equatorial plane. When multiple bodies in a solar system are involved, the ecliptic plane can be used. For intercepting another orbiting body, the orbital plane of the body to be intercepted is used. An orbital plane can be fully described by giving the inclination and the longitude of the ascending node relative to a reference plane.

Semi-major axis

The major-axis is the long axis of an ellipse, and the semi-major axis is half of this. In KSP the semi-major axis is calculated with ${\displaystyle {\text{sma}}={\text{radius}}+{\frac {Ap+Pe}{2}}}$. It's the average of the Apoapsis and Periapsis computed relative to the center of the body. As both are relative to the body's surface, the radius must be added. All orbits with the same semi-major axis have the same period, regardless of their eccentricity.

Sub-orbital

Describes an orbit where the periapsis is below the surface of a planetary body. If a suborbital path is followed for too long the orbiter will collide with the body being orbited.

Thrust-to-weight ratio

→ See also: Thrust-to-weight ratio

${\displaystyle {\text{TWR}}={\frac {T}{W}}={\frac {T}{m\cdot g}}}$The Ratio between the total mass of the vehicle and the available thrust of all propulsion devices of the vehicle/current stage. A TWR greater than 1 means the craft will have enough thrust to accelerate vertically and gain altitude. A TWR below 1 means that the craft won't be able to counteract gravity and drag at low altitudes, although in space it only means that maneuvers will take longer. Because the weight (W) depends on the current gravitational acceleration (g) the TWR depends on which body is currently influencing the craft. The acceleration on the Mun's surface is only 16.6 % of Kerbin's acceleration, so at the surface a TWR_Kerbin = 1 would be a TWR_Mun = 6.

Orientamento della Nave

The ship orientation is always relative to an specific object. The terms are usually defined relative to the cockpit.

Zenith

Top side of the ship which is usually oriented away from the orbited body. Opposite of nadir.

Nadir

Bottom side of the ship which usually oriented towards the orbited body. Opposite of zenith.

Port(side)

Left side of the ship. Opposite of starboard.

Starboard

Right side of the ship. Opposite of portside.

Front

Front side/end of the ship which is usually towards the nose or prograde vector. Opposite of aft.

Aft

Back side/end of the ship which is usually housing the primary rockets and facing in retrograde. Opposite of front.

Manovre nello spazio

Atmospheric Braking

→ Articolo principale: Aerobraking

Lowering the periapsis so it is inside a planetary atmosphere. This will lead to the vessel being slowed by atmospheric drag. Can lead to reentry (see below), but also is used to reduce the necessary burn time for significant orbit alterations.

Burn

firing of the engines, usually to alter trajectory in some way.

Circularizing

A maneuver (firing of the engines) that makes an orbit's eccentricity 0, or close to zero. This is usually achieved by a burn close to an apsis.

Maneuver Node

→ Articolo principale: Maneuver node

Maneuver nodes are a nice tool to plan and project trajectory changes in map view prior to doing the actual burn.

Re-entry

Re-entering atmosphere and using drag to decelerate a vessel to a groundwards trajectory. This usually causes intense heat stress on the object as the vessel requires sufficient speed to not "bounce" back from the atmosphere into space. Currently (0.21.1^[outdated]) re-entry is only partially implemented with effects but heat and bounce are not yet implemented. (There are mods however)

Retroburn

A burn performed "backwards", e.g. with the engines facing towards prograde and nose towards retrogade (hence the name). This is a common maneuver to used to lower the height of the orbit without altering any other orbital parameters.

Fisica

Acceleration

Rate of change to your velocity. Acceleration is a vector, measured in "m/s²".

Ballistic trajectory

A falling object's trajectory is ballistic. In rocketry it usually indicates that the object in question is only influenced by gravity and does not exert any force (ie. thrust) of its own.

Delta-v (Δv)

The change in velocity that has or can be exerted by your spacecraft. This is measured in meters per second (m/s). More mass can reduce the delta-v, while more propulsion can increase it. This makes it a useful value to calculate efficiency of launch vehicles. For example, a launch vehicle requires about 4,000 m/s of delta-v to escape Kerbin's atmosphere and achieve a stable orbit.

Energy

→ See also: Specific orbital energy on Wikipedia

The energy of an object in an orbit is the sum of its potential and kinetic energy. The potential energy is ${\displaystyle E_{p}=-{\frac {GMm}{R}}}$ and kinetic energy ${\displaystyle E_{k}={\frac {1}{2}}mv^{2}}$ where G is the gravitational constant, M is the mass of the body, m is the mass of the craft, R is the distance from the center of the body and v is the velocity. This results in ${\displaystyle E=E_{k}+E_{p}={\frac {1}{2}}mv^{2}-{\frac {GMm}{R}}}$. This sum stays the same when not thrusting: When approaching periapsis potential energy is transferred into kinetic energy. After passing the periapsis the kinetic energy is converted back into potential energy. When the energy or specific orbital energy is greater than zero the vehicle is on an escape trajectory.

There is also the specific orbital energy (${\displaystyle \epsilon }$) which doesn't require the mass of the craft: ${\displaystyle E_{p}=\epsilon _{p}m}$, ${\displaystyle E_{k}=\epsilon _{k}m}$, ${\displaystyle E=\epsilon \,m=(\epsilon _{k}+\epsilon _{p})m=-{\frac {GM}{2a}}}$. All orbits with the same semi-major axis (a) have the same specific orbital energy.

Escape Velocity

The velocity needed to escape a given planet's gravity well, as given by ${\displaystyle v_{e}={\sqrt {\frac {2GM}{r}}},}$ where G is the gravitational constant, M is the mass of the planet, and r is the radius of the planet.

g-force (G)

A measurement of acceleration as expressed in the sea-level force of Earth's gravity with 1 G being about 9.81 m/s². An object at Earth's surface is accelerated at 1 G. The object weighs twice as much when at 2 G acceleration and is weightless when accelerated with 0 G. In free fall, like in orbit, and without an engine running or an atmosphere applying drag all objects experience no acceleration which can be expressed as 0 G.

Gravity

The force exerted by all objects with mass. Very weak. Usually only objects with very high mass - ie. planets, moons - have any noticeable effect. Diminishes with the square of distance from the center of mass. So for an object twice as far, experiences only 1/2² = 1/4 of the gravity.

Gravity Well

The area around a planet affected by gravity. Actually extends to infinity, but as gravity decreases quadratically with distance (if you multiply by 2 the distance, the gravity is divided by 4), it is only significant within the planet's sphere of influence.

Orbit

→ Articolo principale: Orbit

When an object has sufficient tangential velocity (and is outside the atmosphere, so drag won't slow it down) so that it will keep falling "next" to the planet (never touching ground) its trajectory is called an orbit. Stable orbits are elliptical (a circle is an ellipse with zero eccentricity). If the objects tangential speed exceeds escape velocity it's orbit will be either para- or hyperbolic.

Specific Impulse (I_sp)

→ Articolo principale: Specific impulse

${\displaystyle I_{sp}={\frac {T}{\dot {m}}},[I_{sp}]={\frac {m}{s}}}$The I_sp defines how effective a propulsion system is. The higher the I_sp the more powerful is the thrust applied to the rocket with the same fuel mass. The I_sp is usually given in seconds but actually the physically correct unit is distance per time which is usually given in meters per second or feet per second. To avoid confusion which unit of speed is used, the physical correct I_sp (in distance/time) is divided by the surface gravity of Earth (9.81 m/s²). This results in a value given in seconds. To use this I_sp in formulas it must to be converted back into distance per time which requires multiplying with the surface gravity of Earth again. As this value is only used to convert between those two units, the specific impulse doesn't change when the gravity changes. It appears that KSP use a value like 9.82 m/s² and thus using a little less fuel.

As the specific impulse is the ratio of thrust and fuel flow ${\displaystyle {\frac {Ns}{kg}}}$ is sometimes given as the unit. This is mathematically another form of ${\displaystyle {\frac {m}{s}}=kg\cdot {\frac {m}{s^{2}}}\cdot {\frac {s}{kg}}}$ because force is the multiplication of mass and acceleration defining ${\displaystyle N=kg\cdot {\frac {m}{s^{2}}}}$. So ${\displaystyle 1{\frac {Ns}{kg}}=1{\frac {m}{s}}}$ with the later begin simply only in SI base units.

Sphere of influence

The radius around a celestial body where its gravity well is non-neglectable. Commonly known as SoI/SOI.

Tangential velocity

The component of your velocity that's tangential to your trajectory. Instantaneous velocity - velocity when the time of measurement approaches zero - is always tangential to your trajectory.

Trajectory

A trajectory is the path that a moving object follows through space as a function of time.

Velocity

Rate of change of your position. Your speed and direction. Velocity is a vector, measured in meters per second (m/s).

Guarda anche

• Tutorials